Is Your Gut Making You Depressed or Anxious?

Turns out “gut feeling” is more than just a fancy name for intuition. Our small and large intestine, and the trillions of bacteria that call it home, are more important than ever imagined for influencing our mood, our anxiety, our choices, and even our personalities. This week Savvy Psychologist Dr. Ellen Hendriksen goes straight for the gut with three surprising mind-gut connections.

If you had to guess the organ that has undue influence on your emotions, your mood, even your choices, what would you guess? The brain? Sure, but what else? The heart—that mythological seat of the soul? Not quite. The stomach? You’re getting warmer. Would you believe it’s the large and small intestine, collectively known as the gut? More specifically, it’s the trillions of bacteria—the microbiota—that live in your gut. Each of us carries up to four and a half pounds of bacteria around in our guts at any given time. More than 100 trillion microbes live down there. That’s as many cells as make up the rest of your body.

Now, this crowd is mostly good guys, and they do important work, to the extent that some scientists advocate classifying these collective microbiota as its own organ. Aside from helping digest our food, they protect us from disease, neutralize some of the toxic by-products of the digestive process, and make it harder for bad bacteria to set up shop. In short, your gut does way more than just digest everything from Cheetos to camembert.

But it turns out gut bacteria may also affect how we feel. Who knew the next frontier in mental well-being would lead right to the toilet? With that lovely image in mind, here are 3 big ways our microbiota are connected to our mental health.

Connection #1: Your gut-mind relationship goes two ways. We already know that feeling anxious affects our guts. Anxiety make us run to the bathroom, makes us queasy, and generally makes our guts feel like stressed-out Boy Scouts were practicing for their knot-tying merit badge in there. Likewise, when you’re depressed, everything stops in its tracks, resulting in constipation. But while it’s intuitive that anxiety and depression affect the gut, turns out the gut may also affect anxiety and depression.

A research group at University College Cork in Ireland fed Lactobacillus rhamnosus, a probiotic common in yogurt, to one group of mice. To another group, they fed the equivalent amount of a sterile, bacteria-free broth. Then the mice were put through the equivalent of Mouse Boot Camp. When forced to swim in deep water, the probiotic-fed mice persevered. But the broth-fed mice gave up without a struggle, indicating the mouse version of depression. Likewise, when placed in an unfamiliar elevated maze, the probiotic-fed mice ventured out into the open more often than the broth-fed mice. They hung back, a proxy for mouse anxiety. Indeed, the probiotic-fed mice were more chillaxed in every way—that is, until everybody’s vagus nerves were cut, thus severing the most important communication pathway between the brain and the guts. After that, the differences between the two groups vanished.

OK, you say, but we are not mice. We don’t have mouse guts or mouse brains. True, but in another study, this time out of UCLA, a group of healthy women ate probiotic-fortified yogurt twice a day for four weeks. A second group ate a non-probiotic milk product, and a third group ate their regular diet. After the four weeks, everyone went in the brain scanner to measure their brain’s response. The probiotic group showed significantly different brain functioning, both at rest and in response to a task of emotion recognition.

The take home? There’s still a long way to go, but someday, perhaps the way to unwind may not be with a bottle of beer, but with a container of your favorite yogurt.

Connection #2: Your gut may affect your personality. In another mind-blowing (or should I say gut-blowing?) study, a group at McMaster University used two groups of experimental mice, each bred for certain behavioral characteristics. One strain was more timid and shy—you might even say they were introverts. The other was more sociable and bold—you might call them the extroverts. But not for long. The researchers wiped out all the gut bacteria of both strains of mice with antibiotics, then fed each group with the gut bacteria of the opposite mouse strain. What happened? Behaviorally, they swapped personalities. The shy mice became outgoing, the outgoing mice became shy.

Unlike the yogurt study, we’re probably not going to try repeating this one in humans anytime soon. But the trend is clear: our guts play a role in our emotions and perhaps even our behaviors. Which brings us to...